1. Field of the Invention
This invention relates to a power converter apparatus that uses high-speed semiconductor switching devices and includes a snubber circuit for restraining a surge voltage, and especially to a wiring structure of the snubber citcuit.
2. Discription of the Background
In recent years, power semiconductor switching devices for power converters or power inverters remarkably advance inhigh-speedswitching. Forexample, GCT (Gate-communicated Thyristor) is a current gate trigger type of high-speed semiconductor switching device, and IGBT (Insulated Gate Bipolar Transistor) and IEGT (Injection Enhanced Gate Transistor) are voltage gate trigger types of high-speed semiconductor switching devices. These high-speed semiconductor switching devices, which are capable of switching a voltage of 3-6 KV (Kilo-Volts) and a current of 3-4 KA (Kilo-Amperes), have been developed and made practical. Further, since a dV/dt resistance of a semiconductor switching device atatime of turningoff has been improved, it is attempted that a snubber circuit is made smaller in size and less loss.
FIG. 1 is a circuit diagram showing a conventional NPC (Neutral Point Clamped) inverter that uses GTO (Gate Turn-off Thyristor) as a semiconductor switching device. Snubber circuits 2a, 3a, 4a and 5a are respectively connected to GTO switching devices 2, 3, 4 and 5. Each of the snubber circuits 2a-5a restrains a surge voltage generated at switching the GTO switching devices 2-5 and includes a capacitor, a diode and a resistor.
In recent years, as highly efficient GCT, IGBT and IEGT are put to practical use, a cramp snubber circuit or a capacitor are come to be connected to a DC (Direct Current) power source. These high-speed semiconductor switching devices are able to switch off acurrent of several KA (Kilo-Amperes) up to 0 (zero) in 1-2 micro-seconds as a matter of their behavior. At the time of switching off a large current, a surge voltage represented by the product of a wiring inductance and a rise rate of current (dI/dt) is generated. If a peak of the surge voltage or a rise rate of voltage (dV/dt) are beyond capacity to resist voltage of a semiconductor switching device, the semiconductor switching device may be broken for ever. Therefore, it is important that the surge voltage be less than the capacity to resist voltage of the semiconductor switching device.
However, in a large capacity type of power converter that uses high-speed semiconductor switching devices, since either one of a charge and discharge snubber circuit or a clamp snubber circuit is connected to each of the semiconductor switching devices, the power converter becomes large in size and costly. Accordingly, it is desired to provide a device to restrain a surge voltage by only cramp snubber circuit connected to a DC power source in the same way as a power converter using semiconductor switching devices having small capacity to resist voltage. That is, it is desired to provide a device to restrain a surge voltage without attaching a snubber circuit to each of the semiconductor switching devices.